Emma Townshend: The Yellow Book is the best guide to the UK's hidden gardens - and a secret directory of the finest home-made teas

I am terribly motivated by cake. It's a known feature of my character. And I don't think I'm alone. I'm pretty sure my grandma stands firmly with me on the issue. One of the reasons I know this is that when I was about six, on a sunny summer afternoon we'd pull a copy of The Yellow Book from her kitchen drawer and choose a garden to visit from its smeary, newsprinty list, making sure we selected one with "home-made teas". Almost no point in bothering, otherwise.

A horrific number of years later, my grandma and I can still be lured to places by cake. And The Yellow Book, even though it is now printed on entirely smear-free paper, plays a big part in gâteau location.

As an encyclopaedic list of gardens opening for charity in England and Wales, the book is produced by the National Gardens Scheme (the NGS), which also churns out those yellow arrows that tempt you down lanes as April comes into its prime. Good old arrows.

Most of the gardens in The Yellow Book are small, private affairs that open only once or twice a year, and offer a fantastic opportunity for a delectable nosy and a chat, generally giving you change from a £5 note.

The NGS is an impressive and professional affair: a huge money-raiser for charities ranging from Macmillan Cancer Support to Parkinson's UK, with the focus on the kind of supplementary nursing care (such as Marie Curie Cancer Care and hospices) where the NHS sometimes falls financially short. And every bit of its millions of pounds' worth of funding comes from individual quids paid into old-fashioned tin money boxes at gardens: entrance fees, plant sales and the all-important tea and a bun.

If it all sounds a bit old vicarage-y, let me point out that the scheme is also fiercely innovative. Visitors have always wanted to see crazily lovely gardens, full of May promise, but nowadays, they also long to see inspirational gardens a bit more like their own. So it ensures the number of small gardens on show, especially in towns, increases every year. (In Balham, south London, this year the NGS premieres a record-breakingly tiny 3m square plot.) More owners are opening in groups, too, so you don't drive all that way for one risky novelty, but get four or five to choose from.

One of the most intriguing "firsts" for 2014 is The Laskett, celebrated home of historian Roy Strong. Here, Strong has made an extraordinary case for English style in the largest formal garden created in the country since 1945: topiary, clipped hedges, avenues and alleyways, plus temples, statues and sundials, all carried out in a piecemeal fashion that leaves visitors loudly arguing its merits on the way home. The annoyance till now is that it's never been open to anyone who wasn't in a group of 20 or more, so the NGS's triumph is a victory for the lone garden tourist. Join the debate yourself on 7 September.

The NGS is helped by having what I repeatedly find to be a brilliantly useful website. Need a garden with a B&B actually in it? Sure thing. Want to go and look at some good allotments near where you live, to get growing tips? Easily done. Need to check whether the teas are home-made before you drive 40 miles into the Oxfordshire countryside? Oh yes.

This year there are more gardens with stuff for kids (often a trampoline; sometimes chickens). There are more gardens alongside world-class nurseries, so you can painfully splurge afterwards (such as the astonishing Crug Farm Plants, in Wales). There are more gardens belonging to designers, from Chelsea superstar Christopher Bradley-Hole to Tom Stuart-Smith… erm, another Chelsea superstar. In fact, there's just more. Of everything, more, more, more. And most particularly, for my grandma and me, more cake.

For more details: ngs.org.uk